1. Field of the Invention
The present invention relates to a semiconductor device wherein electronic components disposed within a case is sealed with resin such as an intelligent high-power module and, more particularly, to a semiconductor device which is less costly and is small in size, and to a resin to be used therefor and a method of fabricating the same.
2. Description of the Background Art
Electronic components of semiconductor devices include thin-film resistors, ICs, hybrid ICs, transistors, diodes and the like. For increasing the reliability of semiconductor devices under various environmental conditions, the electronic components mounted on a substrate are housed in a package. In the semiconductor art, packages have generally been shifted toward resin packages which are less costly.
Methods of packaging electronic components with resin include transfer molding, casting, dipping, powder coating, dropping, tabletting, potting and the like. In particular, portions and modules having a fine structure are protected by a precoating material (partial protective coat) or a buffer coating material (entire protective coat).
In particular, transistors and hybrid components such as power modules, transistor modules, hybrid ICs are coated with the entire protective coat and are then sealed by pouring and hardening a normal liquid epoxy resin.
For example, power components are generally protected overall using as a buffer coating material a gelatinous material such as silicon gel, and then epoxy resin or the like is poured thereon, to achieve the sealing.
FIG. 3 is a cross-sectional view of a conventional resin-sealed semiconductor device. A semiconductor device 20 comprises electrode terminals 2, elements 6 and wires 7 which are disposed within a case 4 having a base plate 5. The electrode terminals 2, elements 6 and wires 7 are mounted on the base plate 5, and silicon gel 8 are poured so as to surround the mounted portions of the components and bent portions 3 of the electrode terminals 2. Epoxy resin 1 is filled in the remaining interior of the case 4 which overlies the silicon gel 8. Filling the whole interior of the case 4 with only the normal epoxy resin decreases the reliability of the device due to the stresses generated when the resin is hardened and the effects of impurity ions. Thus the silicon gel 8 serving as a buffer is used.
However, the silicon gel is costly and requires the pouring and hardening processes thereof, resulting in high costs for providing the semiconductor device 20. Another problem is the difficulty in size reduction in the direction of the thickness because of the two-layer structure having the silicon gel 8 and the resin 1.